The n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid, are bioactive molecules with clinical applications for suppressing chronic inflammation. A major obstacle in the translation of n-3 PUFAs into the clinic is a limited understanding of the mechanisms by which n-3 PUFAs regulate inflammation and moreover, the consequences of n-3 PUFAs on other aspects of the immune system. We have discovered n-3 PUFAs boost murine immune responses from B cells, which we propose is a result of n-3 PUFAs exerting immunosuppressive effects on antigen presenting cells and CD4+ T cells. The data raise the exciting possibility that n-3 PUFAs can be used to simultaneously suppress cell-mediated inflammation and enhance humoral immunity in select diseases. The long-term goal of our research program is to establish the efficacy of n-3 PUFAs on immunity for the general public and for specific clinical populations. The current objectives are to determine the individual and combined efficacy of EPA and DHA in regulating inflammatory cytokines and humoral immunity in lean and obese mice. The rationale for focusing on obesity is that obese individuals display, in addition to chronic inflammation, poor humoral immunity. The central hypothesis is that n-3 PUFAs generate CD4+ Th2 cytokines that boost B cell activation and antibody production. We will also test the additional hypothesis that n-3 PUFAs enhance Th2 cytokines and B cell activity by targeting the G-protein coupled receptor (GPR) 120, an n-3 PUFA sensor. Aim 1 will establish n-3 PUFAs suppress Th1/Th17 cytokines and enhance Th2 cytokines and Tregs in lean mice. Aim 1 will then determine if n-3 PUFAs boost Th2 cytokines by targeting the immunological synapse and GPR120 of select cell types. Aim 2 will determine how n-3 PUFAs boost humoral immunity of lean mice. Aim 2 will first elucidate how elevated Th2 cytokines, in response to n-3 PUFAs, enhance B cell activity. Aim 2 will then dissect the contribution of additional mechanisms by which n-3 PUFAs could directly enhance B cell activity. These include n-3 PUFAs stimulating B cell GPR120 signaling and generating pro-resolving lipid mediators. Aim 3 will establish the efficacy of n-3 PUFAs in rescuing the decrement in antibody production of obese mice in response to several antigens including influenza. Aim 3 will also establish the efficacy of n-3 PUFAs on suppressing inflammation by enhancing select adipose specific B cells in a GPR120 dependent manner. The approach will rely on immunological assays, genetic mouse models, lipidomics, and biophysical imaging methods. The proposal is significant because it will define the efficacy of EPA+DHA (modeling over-the-counter and prescription supplements) and the individual activities of EPA and DHA on inflammation and humoral immunity in lean and obese mice. The research is innovative because it tests novel mechanisms using complementary approaches to challenge the general paradigm that n-3 PUFAs only have utility for suppressing or resolving inflammation. Completion of the project will provide a foundation for studies with select n-3 PUFAs on immunity in humans.